1. Field of the Invention
The present invention relates to a horizontal axis wind turbine and a method for controlling a horizontal axis wind turbine.
2. Description of Related Art
In recent years, horizontal axis wind turbines have been proposed and in practical use in order to generate electric power from natural wind. Such a horizontal axis wind turbine is provided with an anemometer for measuring the wind speed blowing against a rotor (wind speed) and a yaw sensor, such as a yaw vane, for measuring the direction of the wind blowing against the rotor (wind direction). In the case that a value of the wind speed measured by the anemometer rises above a predetermined value, a control device of the horizontal axis wind turbine starts rotation of the rotor as well as rotates the rotor axis in a substantially horizontal plane in such a way that the rotor faces to the wind direction measured by the yaw sensor.
By the way, the control device of the horizontal axis wind turbine controls the rotor so as to stop a power generation action automatically when the anemometer or the yaw sensor breaks down and becomes unable to measure the wind speed or the yaw angle. In the case that the anemometer or the yaw sensor breaks down this way, much time and cost are required until recovery since horizontal axis wind turbines are generally installed in remote locations. If the stop period of power generation action is protracted, a loss of electric energy to be generated for the period becomes serious.
Therefore a plurality of anemometers and yaw sensors are provided for a breakdown of one anemometer (or one yaw sensor) in an earlier development. (For example, see Nordex AG, “Products & Service Onshore N50”, [online], Nordex AG.
However provision of a plurality of anemometers and yaw sensors causes increase of cost for them. Therefore arts to prevent the stop of power generation action at low cost without employing a superfluous anemometer and yaw sensor have been longed for.